I have finished the clean builds and while it is now creating the new mesa directory inside of lib and putting libGL.so and other libraries in there, when paraview is run with
paraview-mesa paraview --backend llvmpipe --print
paraview is still not using that libGL.so that is now in the lib/mesa directory and is instead still attempting to use a nonexistant nvidia driver (and thus failing). Your distributed binaries do not have this problem, and correctly use the Mesa compiled lib. Why is paraview ignoring the library that it built and installed?